An essential step in the life cycle of HIV-1 and other retroviruses is the nuclear import of the preintegration complex, a replication intermediate carrying the viral genome. During the subsequent productive phase of the life cycle, Gag proteins, precursors to the structural proteins of the viral core, travel to the plasma membrane where virion assembly and release occur. The transport mechanisms involved in these aspects of retroviral replication have not been identified. In the life cycle of many viruses, elements of the cytoskeleton are involved in the transport of viral proteins and structures. They have found evidence that HIV-1 Gag proteins interact directly with the cytoskeleton. The general objective of this application is to further examine interactions between HIV-1 and the cytoskeleton and determine their role in viral replication. These interactions may be involved in cell to cell transmission of virus, in the assembly of virus particles, and determine the ability of HIV-1 replicate in certain cell types involved in disease pathogenesis. The Specific Aims are: 1) to identify the cytoskeletal structures which interact with the HIV-1 Gag proteins, 2) to identify the HIV determinants of interaction with the cytoskeleton, and 3) to examine the role of the cytoskeleton in HIV-replication.